<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        var arr = {
            A:[{city:"武汉"},{city:"广州"}],
            B:[{city:"深圳"},{city:"广州"}],
            C:[{city:"上海"},{city:"武汉"}]
        }
        // var list=[];
        // for(var k in arr){
        //    list.push(...arr[k])
           
        // }
        // var res = []
        // list.forEach(item=>{
        // if(!res.includes(item.city)){
        //     res.push(item.city)
        // }
        // }) 
        // console.log(res)
        var values = Object.values(arr);
        var res = []
        values.forEach(item => {  
            item.forEach(city=>{
                if(!res.includes(city.city)){
                    res.push(city.city)
                }
            })
        });
        console.log(res)//(4) ['武汉', '广州', '深圳', '上海']
    </script>
</body>
</html>